Battery Dies With Accessories

Got a question. I have a 2002 Rendezvous. Ever since yesterday, when I leave my XM plugged into the cigarette lighter, it kills the battery after about ½ hour. Mind you I have had my XM for over a year. I leave the cradle plugged in and sometimes remove that actual radio, or sometimes I leave the radio in but powered off. Yesterday after I went to get back in it after about ½ hour, it was dead. I unplugged the XM and check the cords and it started with no problem. I left it unplugged all night and it started fine this morning. I plugged in the XM and after an hour the battery was dead again. I unplugged it and wiggled the battery wires and it starts.

It seems the cigarette lighter is making it pull juice or something. Can anyone help?